1. Field of the Invention
The present invention relates to a perforation gun with a partially hollow carrier aspect.
2. Description of the Prior Art
After a well is drilled and casing has been cemented in the well, one or more formation zones of interest may be found. Unless the casing, cement, and formation are penetrated, fluid found within the formation zone cannot flow into the well. Oil and gas well operators have, therefore, found it necessary at times to perforate the well casing, cement, and surrounding formations in order to bring the well into production.
Several devices are known in the art to help accomplish this task. One such device, a perforation gun, comprises a strip of high energy explosive charges that may be lowered into the well to the desired depth. These charges are often phased to fire in multiple directions around the circumference of the wellbore. When fired, these charges create explosive jets that penetrate the well casing, cement, and formation. Production fluids in the perforated formation may then flow through the perforations and into the wellbore.
Some perforation guns are comprised of a strip of shaped charges held in a predetermined position within a charge holder. Such charge holders may or may not be contained within an elongated, cylindrical carrier. When found within such a carrier, non-capsule shaped charges are used. These charges are pressure sensitive and, therefore, must be contained within a pressure sealed carrier. The charges are typically positioned within such a carrier so that they are aligned in a pattern to allow each charge to penetrate a different portion of the casing. Because the charges, once detonated, penetrate the carrier as well as the casing, the carrier may become deformed. In such a case, the perforation gun may become lodged in the wellbore and difficult to retrieve.
In an effort to eliminate this problem, some prior art perforation guns contain charges aligned with thinner areas of the carrier. These thinner areas, or scallops, maintain the pre-detonation carrier pressure seal, but allow the charge, upon detonation, to more easily penetrate the carrier body. Scalloped perforation guns still require the charge to penetrate the carrier which reduces the amount of force entering the casing. Unfortunately, because of internal pressures generated within the gun during detonation, scalloped carriers may become deformed. In an extreme case, a scalloped carrier gun may, before detonation, lose its pressure seal, thus exposing the non-pressure sealed charges to wellbore fluids. Upon detonation, severe and even catastrophic damage to the carrier and wellbore may result.
An additional known problem with scalloped carrier perforation guns involves aligning the charges with the scallops. A sealed carrier prevents the user from visually confirming that the charges are properly aligned with the scallops. Therefore, occasionally a scalloped carrier perforation gun is improperly armed because the charges are directed at non-scalloped areas. This results in, upon detonation, severe damage to the carrier and inadequate casing penetration.
In an effort to reuse the carrier, some perforating guns are comprised of a cylindrical carrier with removable port plugs aligned with the charges, to seal the gun. These types of guns use non-capsule shaped charges. However, these plugs are known to occasionally allow well fluid to enter the gun, which may cause severe damage to the carrier upon detonation.
Other perforation guns are comprised of charges mounted on the gun carrier which is normally a retrievable strip section. The charges used in these guns are capsule shaped charges which are pressure sealed. Capsule shaped charges are individually mounted within the carrier wall with threaded or other type couplings. Because of the forces acting at different directions during detonation and because of weaknesses in the strip, these guns may suffer damage upon detonation and become difficult to retrieve.
Other perforating guns are comprised of charges mounted in a weak expendable gun carrier (normally wires), which are totally destroyed upon detonation and left in the well. The charges used in this type of gun are capsule shaped charges which are pressure sealed. Because of weaknesses in such gun carriers, it is sometimes difficult to lower the gun to the desired depth. These guns also have a high potential of becoming lodged within the wellbore prior to detonation. Additionally, following detonation, all of the contents of the gun, including the charges and gun carrier, form debris which is necessarily, but undesirably, left in the well.
What is needed is a perforation gun that is easily assembled and armed, permits a maximum amount of charge energy to penetrate the casing, cement, and formation, is retrievable, prevents debris from accumulating in the wellbore after detonation, and has a reusable carrier that is not deformed after detonation.